Explosive



A. C; SCOTT June 26, 1934.

EXPLOSIVE L EH -mmmimmm -I--- Filed NOV. 5, 1932 Patented June 26, 1934UNITED STATES EXPLOSIVE Alexander Cruickshank Scott, Faversham, England,assignor to Heaters Limited, London, England, a British companyApplication November 3, 1932, Serial No. 641,127 In Great BritainNovember 11, 1931 14 Claims.

. 'I'his invention comprises improvements in or relating to explosives.It is known to provide explosive cartridges consisting of a strong metalcontainer filled with carbon dioxide or like gas under pressure and acartridge which can be ignited in the carbon dioxide or the like so asto raise its temperature to such a point that the pressure within thecontainer is adequate to burst a retaining disc or other part of thecontainer and so bring about an explosion of controlled force. Suchcartridges have proved very valuable as mining explosives, but theprovision of a suitable heating cartridge oifers difficulties. Thecomposition of the heating cartridge is usually that of someself-combustible explosive, such for example, as a perchlorate explosivecontaining a fuel and capable of being ignited by means of anelectrically operated match. Ordinary fuels, used in such mixture, suchas kerosene, however, prove to be soluble in liquid carbon dioxide andare, therefore, removed from the heated cartridge by the CO2 in thesurrounding container thus destroying the self-combustible properties ofthe heater. Attempts have been made to provide heating cartridges whichare not subject to this disadvantage by encasing the cartridges in animpermeable envelope, for example, a lead tube, but this leads tocrushing the cartridge by the external pressure and is not satisfactory.

According to the present invention a heating mixture for an explosive ofthe kind described is constituted by a mixture of an oxygen-carryingsalt, for example potassium perchlorate, and a non-explosive ornon-inflammable cellulose ester, for example cellulose acetate. Themixture of potassium perchlorate and cellulose acetate in finelypowdered form is not, in itself, an explosive in the open air but burnsvery slowly, although it can be detonated if confined. Consequently themixture has a high degree of safety during manufacture. Under theconditions of pressure obtaining within the gas filled container,however, combustion is found to be practically instantaneous, and as thecellulose ester is not soluble in the compressed gas, the mixtureaffords a satisfactory solution of the chiliculty referred to.

In some cases it may be desirable to accelerate the rate of combustionof the heater and according to a further feature of the presentinvention there is incorporated in a heater composition comprising amixture of an oxygen-carrying salt such as potassium perchlorate and anonexplosive or non-inflammable cellulose ester, such as celluloseacetate, a quantity of a resinous substance which is insoluble in liquidcarbon dioxide.

The preferred resinous substance is a synthetic resin of thephenol-formaldehyde type.

This may be admixed with the other ingredients in the form of a liquid,thinned with a solvent if required, but preferably in this case thesolvent should be one which does not attack the cellulose ester. Forexample the solvent may consist of alcohol which comprises only a smallproportion of acetone.

The composition is dried or warmed after the incorporation of the resinin order to solidify the resin.

Inert silicates or the like, for example, asbestos fibre, talc, mica,French chalk or fullers earth may, if desired, be mixed into the heatingmixture for the purpose of assisting uniformity of combustion.

One very advantageous use of the heating mixture of the presentinvention is in connection with blasting cartridges of the type shown inUnited States Patent No. 1,805,541, Dent Ferrell and Arthur W. Helmholtzand for the purpose of illustration the present invention is hereinshown as applied to a cartridge of this general type.

The drawing is a view in longitudinal section of a blasting cartridge ofthe type referred to and showing the improved heating mixture of thepresent invention applied thereto.

Referring to the drawing it will be noted that the present invention isdisclosed as embodied in a cartridge comprising a casing 10 having arupturable disc 11 and a directing cap 12 at the discharge end, andmeans 13 for establishing an electrical connection for the heatingelement and for introducing the blasting medium into the interior 14 ofthe cartridge. The cartridge construction will not herein be describedin detail inasmuch as it is substantially the same as that shown in theUnited States patent referred to above.

The tubular heat producing unit 15 containing the heating mixture isadapted to be inserted in 100 the position shown in the drawing with itselectrical contact 16 at one end thereof in contact with the rupturabledisc 11 and the electrical connection 17 and at the opposite end thereofin contact with the plate 18 constituting the other 105 terminal for theelectrical circuit.

The following are examples of the preparation of mixtures according tothe present invention.

Example 1 Finely powdered potassium perchlorate having a largeproportion of particles less than 200 mesh is mixed with similarlypowdered cellulose acetate and asbestos fibres in the followingproportions:-

Per cent Potassium perchlorate 74 Cellulose acetate 24 Asbestos fibr 2These ingredients are mixed in an ordinary kneading or mixing machineuntil they are thoroughly incorporated. They are then made up into papercartridges containing a powder match capable of ignition by an electricfuse.

The terminals of the fuse are suitably connected to contact elements onthe ends of the cartridge and the cartridges introduced in known mannerinto a carbon dioxide container of the kind hereinabove referred to.After the container has been charged with carbon dioxide it can beexploded by igniting the mixturethrough an electric current applied tothe fuse.

Example 2 A similar mixture is prepared to that set forth...

in Example 1, but'is moistened by acetone and rolled into sheets. Uponbreaking up the sheets, a granulated heating mixture is obtained whichcan be used in a similar way to the powdered mixture.

Example 3 Example 4 There are mixed together:

Parts Potassium perchlorate KCLO4 (finely powdered) Cellulose acetateE10 resin Elo" resin which is a phenol formaldehyde condensation productin the soluble stage of condensation is thinned with a liquid consistingof ethyl alcohol containing a small quantity of acetone. The celluloseacetate and the potassium perchlorate are first mixed with one anotherand thereafter the liquid resin is added with stirring. Theincorporation of the resin makes the compound somewhat granular, as semof the particles of the powdered constituents are caused to adheretogether. After incorporation of the resin and stirring, the mixture iswarmed and dried to remove the solvent and is then in granularcondition, or if suflicient of the solvent is initially added with theresin the mixture makes a softish friable cake which is, after dryingeasily crushed to a fine-grained powder. The granular or powderedmixture is then filled into cartridges and utilized as heating elementsin explosives of the known type containing carbon dioxide.

The following tests were carried out with the heating cartridge ofExample 4 filled into carbon' dioxide cylinders:-

40 grams of the mixture in a cylinder containing only five ounces of CO2failed to shear the steel sealing disc (7/64 of an inch thick) on theend of the cylinder. 40 grams, in a series of ten tests, sheared thedisc twice when only 6 ounces of CO2 were present. Thus about 7 ouncesof CO2 is the minimum for certainty of shearing when 40 grams ofexplosive are used. A charge of 40 grams is a normal one for this heaterfor a (302 container of the size employed in these tests and the normalquantity of carbon dioxide would be about 10 to 12 ounces. It will,therefore, be seen that the explosion is sufliciently yiolent when theresin is incorporated to ensure rupture of the disc, even when thecarbon dioxide contained in the cylinder has fallen away, as sometimeshappens through leakage, to a value as low as 7 ounces and thus failureto explode is very unlikely which is not the case when the resin isomitted. If it is desired to ensure explosion with still smallerquantities of CO: this can easily be arranged by increasing the charge.However, with the quantities stated, should all or nearly all the C9:have leaked away, there is fair certainty that the disc will not besheared, and this is an advantage.

In this application, the term gas is intended to include vapors orgaseous substances which may pass into the liquid state under theconditions of temperature and pressure obtaining in everyday use.

I claim:

1. In an explosive charge, the combination of a container adapted towithstand a high internal pressure, a relatively readily-rupturableclosure therefor, a compressed non-combustible gas therein, and aheating element therein comprising a mixture of an oxygen-carrying saltand a non-explosive cellulose ester.

2. In an explosive charge, the combination of a container adapted towithstand a high internal pressure, a relatively readily-rupturableclosure therefor, a compressed non-combustible gas therein, and aheating element therein comprising a mixture of an oxygen-carryingsaltaud a non-inflammable cellulose ester.

3. In an explosive charge, the combination of a container adapted towithstand a high internal 1 pressure, a relatively readily-rupturableclosure therefor,, a compressed non-combustible gas therein, and aheating element therein comprising a mixture of potassium perchlorateand a 4. In an explosive charge, the combination of a container adaptedto withstand a high internal pressure, a relatively readily-rupturableclosure therefor, a compressed non-combustible gas therein, and aheating element therein compris- 1 ing a mixture of potassiumperchlorate and cellulose acetate.

5. In an expl sive charge, t e combination of a container adapted towithstand a high internal pressure, a relatively readily-rupturableclosure" 1 therefor, a compressed non-combustible gas therein, and aheating element therein comprising a mixture of an oxygen-carrying salt,a nonexplc ve cellulose ester, and a resinous substance which isinsoluble in carbon dioxide. 1

6. In an explosive charge, the combination of a container adapted towithstand a high internal pressure, a relativelyreadily-rupturableclosure therefor, a compressed non-combustible gw therein, and a heatingelement therein compris- 1 ing a mixture of an oxygen-carrying salt, anonexplosive cellulose ester, and a synthetic resin of thephenol-formaldehye type.

7. In an explosive charge, the combination of a container adapted towithstand a high internal pressure, a relatively readily-rupturableclosure therefor, a compressed non-combustible gas therein, and aheating element therein comprising a mixture of an oxygen-carrying salt,cellulose acetate, and a resinous substance which is insoluble in carbondioxide.

8. In an explosive charge, the combination of a container adapted towithstand a high internal pressure, a relatively readily-rupturableclosure therefor, a compressed non-combustible gas therein, and aheating element therein comprising a mixture of an oxygen-carrying salt,cellulose acetate, and a synthetic resin of the phenolformaldehyde type.

9. In an explosive charge, the combination of a container adapted towithstand a high internal pressure, a relatively readily-rupturableclosure therefor, a compressed non-combustible gas therein, and aheating element therein comprising a mixture of potassium perchlorate, anon-explosive cellulose ester, and a resinous substance which isinsoluble in carbon dioxide.

10. In an explosive charge, the combination of a container adapted towithstand a high internal pressure, a relatively readily-rupturableclosure therefor, a compressed non-combustible gas therein, and aheating element therein comprising a mixture of potassium perchlorate, anonexplosive cellulose ester and a synthetic resin of thephenol-formaldehyde type.

11. In an explosive charge, the combination of a container adapted towithstand high internal pressure, a relatively readily rupturableclosure therefor, a compressed non-combustible gas therein, and aheating element therein consisting of granules, each granule comprisingcrystals of an oxygen-carrying salt and particles of a nonexplosivecellulose ester bound together by a resinous binder.

12. In an explosive charge, the combination of a container adapted towithstand high internal pressure, a relatively readily rupturableclosure therefor; a compressed non-combustible gas therein, and aheating element therein consisting of granules, each granule comprisingcrystals of potassium perchlorate and particles of a non-explosivecellulose ester bound together by a resinous binder.

13. In an explosive charge the combination of a container adapted towithstand high internal pressure, a relatively readily rupturableclosure therefor, a compressed non-combustible gas therein,and a heatingelement therein consisting of granules, each granule comprising crystalsof an oxygen-carrying salt and particles of cellulose acetate boundtogether by a resinous binder.

\ 14. In=an explosive charge, the combination of a container adapted towithstand high internal pressure, a relatively readily rupturableclosure therefor, a compressed non-combustible gas therein, and aheating element therein consisting of granules, each granule comprisingcrystals of potassium perchlorate and particles of cellulose acetatebound together by a resinous binder.

ALEXANDER CRUICKSHANK SCOTT.

